Subway noise on a platform at the Union Square station was the ear-splitting loudest in the city, according to a City Council new report on the most deafening places.

Of 14 sites measured by the council, the noise was loudest at the 4-5-6 platform of Union Square, where the sound of screeching train brakes on a curve reached as high as 98.6 decibels.

Prolonged exposure to noises louder than 90 decibels can cause permanent hearing damage, according to the National Institute of Health. By comparison, the average conversation registers at about 60 decibels, while a noisy restaurant or heavy traffic pounds the ears at 85 decibels.

Five of the measured spots – including a street corner underneath the 7 train at Queens Plaza and the 4 train platform at Fordham Road in The Bronx – registered higher on the decibel meter than roads near the runways at JFK and La Guardia airports.

“The federal government has spent hundreds of millions of dollars to alleviate noise levels at airports around the city,” said Councilman Eric Gioia, who spearheaded the investigation. “Yet the New York Transit Authority has spent little if anything to alleviate the negative effects of subway noise.”

But transit officials pointed out the average amount of noise on subway platforms has fallen by 10 decibels in the last 20 years.

In a written statement, the Transit Authority pointed to the 1982 Rapid Transit Noise Code Act requiring the authority to perform an abatement study, outline strategies for meeting lower sound levels and write up annual progress reports. Since then, average decibel levels underground have dropped from a brain-busting 98 to a lower – but still dangerous – 88.

Gioia would like to see the Transit Authority take steps to give subway riders some peace and quiet. Their recommendations include requiring the city to purchase only subway cars that employ quieter wheel systems and giving property tax breaks to landlords in noisy neighborhoods who use city-approved noise-reduction methods.

Gioia also took a shot at Mayor Bloomberg’s highly touted 311 non-emergency phone line, saying, “A call to 311 about the MTA will only fall . . . on deaf ears.”

Americans appear to be losing their hearing at a higher rate than in the past. The hearing-failure rate for women between the ages of 60 and 69 increased by 25 percent from 1981-2000.

The rate for men in that age group was up 15 percent in the same time period, according to A League for the Hard of Hearing.